In most Bay Area startup love stories—young, ambitious entrepreneur meets older, wiser, wealthier backers—the former is at least old enough to toast his new deal at a bar. But tech’s latest darling can’t: Sahil Lavingia is just 19. Yet this guy (OK, kid) has already left a red-hot startup, Pinterest, for his own venture, an online payment system called Gumroad that VC firm Kleiner Perkins Caufield & Byers gave him $7 million to develop.

Lavingia wasn’t one of those high-achieving geeks who always dreamed of starting their own company; he spent much of high school messing around with Photoshop and designing iPhone apps in his bedroom. His family moved around the world so much during his early years that he swears he’d never even heard of Silicon Valley until he was 16 or 17.

College (at USC) was also more of a distraction from his real interest (“building things”), until he got an email from Ben Silbermann, who had just received funding for Pinterest. Silbermann was impressed with a data-tracking app Lavingia had developed in high school and written about on his blog, and he wanted the lad to be part of his founding team. Lavingia didn’t hesitate. “I thought it would be more fun than school and help me figure out what I wanted my career to be,” he says.

But even Pinterest, now the third most popular social media site on the Web, didn’t hold Lavingia’s attention for a full year. “I have the rest of my life to make millions of dollars; I’d rather have fun and work on ideas and designs now,” he says. So just as Pinterest was taking off last August, Lavingia gave two weeks’ notice in order to start Gumroad, which he hopes will give PayPal and Amazon a run for their money.

Where does he see himself in 10 years, at an age when, these days especially, most people would be lucky to be starting their career? “I have no idea beyond the next two years—my life changes too fast to plan that far ahead.”